Since the stratigraphy of the Boso peninsula, Chiba prefecture was first undertaken by T. Mitsuchi (1937) in his geological map "Mobara ", many authors have contributed to the geology and paleontology of the region. Among then, K. Kawai (1961) in particular had contributed to the economic geological study on the southern Kanto gas-producing region. Recently Y. Ishiwada, Y. Higuchi and the writer (1962) published the correlation by the smaller foraminifera on the southern Kanto gas field. Surface and subsurface exploration for the natural gas during recent years made the environmental condition of the Kazusa Group on the Boso peninsula clear. The purpose of this report is to describe the correlation of the subsurface biostratigraphy in the northern peninsula to that of the type rout (middle and eastern part of the Peninsula) by the smaller f oraminif era and clear the environmental condition under which the formations was deposited.
The data contain the experimental result on the elimination of the sand in drilling mud by the use of cyclone, which made it possible to get the right size of the feed, the over flow orifice size and the under flow orifice size to the optional body diameter of cyclone in the case of the high viscosity fluid like drilling mud.
By the use of caliper logging the diameter of a drilled well is measured quantitatively. Combining these results with geology and drilling method, the conclusions about the heaving are obtained as follows: (1) There are two causes for the heaving: the property of stratum and the drilling method. (2) Certain stratum has tendency to heave. It depends on clay mineral in the stratum. (3) Stratum heaves under unfavorable drilling conditions such as a slow drilling rate, reaming, and the use of unsuitable mud fluid.
Both theoretically and experimentally a research on three viscometers was carried out. 1. By the use of V-G meter the relationship between the density of mud fluid and the rheological properties such as plastic viscosity, yield volue and gel strength is obtained. 2. There is a certain relationship between the volue obtained by Marsh Funnel viscometer and the plastic viscosity divided by the density. 3. The apparent viscosity measured by Stormer viscometer is between the apparent viscosities measured at 300rpm and 600rpm by V-G meter.